Movie Magic Conjured by Science

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The next time you take in a movie, you may be getting a lesson in
cutting-edge physics without even knowing it. Hollywood has
embraced the complex field of fluid dynamics, the study of how
water, air, smoke and other fluids move, in a big way, allowing
filmmakers to create realistic scenes of turbulent oceans and
falling buildings -- not to mention the quirks of Jeff Bridges'
face.

"It used to be that the story was limited by the technology,"
said Doug Roble, creative director at Digital Domain, a Hollywood
special effects studio. "Now we're getting to the point where
there are no limits. If I want to have Mount Everest fall into
the ocean and catch on fire, we can do that. And the audience
will buy that it is happening."

Computer scientists like Roble are using new kinds of software
programs that harness mathematical algorithms that describe
chaotic scenes of nature. These same kinds of mathematical
formulas can be used to describe and then animate the bending of
steel girders, as seen when downtown Los Angeles collapses in
last year's blockbuster "2012."

Instead of just drawing a steel girder from a building and
pushing it around, Roble says mathematical equations now
determine how the object will move on screen.

"In order to get the physics right, the mathematics is very
stiff," Roble said. "So in order to simulate it accurately, you
have to take extremely small time steps to move the simulation
forward. If it's too fast, the simulation will explode, negative
signs start appearing, and your simulation won't mimic reality."

Canadian computer scientist Robert Bridson wrote about this
emerging field of physics and animation recently in the journal
Science. Bridson's company Exotic Matter has a long list
of Hollywood film projects, including recent "Harry Potter and
the Half-Blood Prince," "Hellboy" and "Quantum of Solace." He's
an expert of sorts in creating realistic smoke, water, fire,
hair, skin and clothing.

"(Digital filmmaking) has a lot in common with foundational work
with applied mathematics and computational physics," Bridson said
from New Zealand, where he's working on the latest Tolkien film,
"The Hobbit." "People will look at a phenomenon of interest and
come up with equations to describe what they are seeing. A lot of
that is now going on in film."

Bridson said creating realistic sea foam and ocean spray has
become the latest challenge for math-based special effects
designers. He notes a particular complex shots of a both a giant
wave and the lion's rippling fur in the just-released fantasy
film "Chronicles of Narnia: Voyage of the Dawn Treader" that made
heavy use of new fluid dynamics-based programs.

What's been driving the marriage of math and movie-making is the
rising expectations of film directors and the availability of
cheap computing power needed to run the software. That means big
special effects no longer equals big budgets.

Using computer simulation of solid and fluid dynamics is both
cheaper for the director and less dangerous for human actors,
Bridson said.

Both Roble and Bridson say the next step for creative programmers
is creating digital doubles for human actors. By using a fully
animated digital character, a director will be able to redo
difficult scenes without rebuilding a set or requiring dangerous
stunts.

In the recent "Tron" sequel, filmmakers wanted to recreate actor
Jeff Bridges' character to resemble what he looked like 30 years
ago. Using new software, they mapped Bridges' current face with a
set of points, then transferred it to images taken from Bridges
circa 1982. The data was crunched using software that wasn't
available a few years ago, Roble explained.

"The human face is extraordinarily tough," Roble said. "Right
now, the research community is focused on muscles and skin."